The present invention relates generally to a method of producing aldehydes. More particularly, the present invention relates to a method of producing aldehydes using a hydroformylation reaction wherein the formation of high boiling point components and decomposition of the catalysts, and in particular the ligand are minimized. The aldehydes produced may be an end product, or alternatively may be an intermediate product employed in further processing.
The production of aldehydes is an important process in the chemical industry. Aldehydes are widely used for a variety of purposes, for example as a precursor for the formation of 2-ethyhexanol (2EH) which is an important raw material for plasticizer, or upon subsequent hydrogenation to form alcohols. Aldehydes may be produced by a variety of methods. One important production method is hydroformylation. The hydroformylation reaction basically combines an alkene with carbon monoxide and hydrogen, in the presence of a catalyst, to form an aldehyde of one carbon number higher than the feed alkene. For example, the hydroformylation of propylene forms butyraldehydes, also referred to as C4 aldehydes. Examples of some prior art hydroformylation processes are described in U.S. Pat. Nos. 4,599,206; 4,748,261; 4,885,401; 5,059,710; 5,288,918; 5,648,553; 5,663,403; and 5,672,766.
In general the prior art hydroformylation systems typically involved the production of aldehydes, and optionally alcohols by further hydrogenation of the aldehydes, by reacting an olefinic compound with hydrogen and carbon monoxide in the presence of a catalyst, most often a metal organophosphorus ligand compound catalyst. A solvent may be employed to dissolve and disperse the reactants in solution thereby providing a reaction solution. The prior art systems are typically a liquid recycle system, that is at least a portion of the reaction solution is withdrawn from the hydroformylation reactor containing aldehyde products along with remaining reactants and catalyst either continuously or periodically. The aldehyde products, and optionally one or more of the reactants and catalyst, are separated in what is generally termed a separation system. The separation system includes a downstream catalyst process path, which is the path the catalyst is exposed to during separation and/or recovery from the reaction solution. FIG. 1 is one illustrative example of such a prior art hydroformylation system. In FIG. 1 the reactor is designated as numeral 10 and the separation system is generally designated as numeral 12. Generally, the reactor 10 includes a continuous stirred tank reactor (CSTR). Optionally, additional equipment may be employed as part of the reactor 10 to increase the conversion of the olefinic compound to aldehydes. To produce C4 aldehydes, feed propylene (PPY) is conveyed via first inlet means to the reactor 10. Hydrogen (H2) and carbon monoxide (CO), often supplied as a gas mixture, better known as oxo gas or synthesis gas are typically introduced via a second inlet means to the hydroformylation reactor 10 or its associated additional equipment. Generally, the H2 and CO concentration in the oxo gas is about 1:1 molar ratio. The main controlling limitation for the overall propylene conversion is the purity of the propylene or synthesis gas feed stream. If the feed stream is of low purity, then the overall conversion of propylene to C4 aldehydes becomes lower. In the instance where the low purity propylene or synthesis gas is used with its low conversion, additional equipment suitably adapted to provide further conversion of the propylene or synthesis gas may be employed. Thus, while the reactor 10 is shown simply as a block in FIG. 1 the reactor may include various unit operations commonly employed in conventional hydroformylation reactor systems.
The aldehyde products are generally separated and recovered from the reaction solution in the separation system 12. Many types of separation systems 12 are utilized in the prior art hydroformylation systems. For example the aldehyde products may be separated and/or recovered from the hydroformylation reaction solution by composite membrane techniques, or optionally by the more commonly used vaporization separation techniques of distillation, such as single or multiple stage distillation under reduced, normal or high pressures, as applicable in an aldehyde removal unit 14. Condensation of the volatilized materials and separation and further recovery thereof may be carried out by conventional means, and the remaining reactants and optionally additionally the solvents contained within the reaction solution may be separated in solvent recovery unit 16 and recycled back to the hydroformylation reactor. Such types of continuous hydroformylation systems are well known in the art and thus need not be described in further detail here. Examples of such continuous prior art systems can be found in U.S. Pat. Nos. 5,087,763 and 5,865,957.
These continuous hydroformylation systems suffer from the build-up of detrimental by-products. Specifically, during the hydroformylation process, other reactions occur in addition to the formation of aldehydes. Many higher boiling point components such as dimers, trimers, tetramers of aldehydes and the like are formed as a by product of the reaction. These high boiling point by-product components (hereinafter referred to as xe2x80x9chigh boilersxe2x80x9d) are detrimental to the process and severely reduce the aldehyde yield. Thus, in the prior art systems it is necessary to remove them from the hydroformylation reactor effluent stream. The high boilers are removed in a variety of conventional techniques, such as by employing one or more a high boiler separation units, such as that described in U.S. Pat. No. 5,648,554, where vaporization or distillation in one or more stages distillation under normal, reduced or elevated pressures is used. Thus, it is highly desirable to provide a method wherein the formation of high boilers are reduced and/or minimized.
An important aspect of the hydroformylation process is the catalyst utilized to assist the hydroformylation reaction. It is common to use a soluble complex of an element selected from Groups VIII to X of the Periodic Table (hereinafter referred to as a xe2x80x9cGroup VIII metalxe2x80x9d) having an organic phosphorus compound as a ligand. In general, the ligand used together with the metal component of the catalyst gives substantial influence to the catalytic reaction. Rhodium (Rh) is commonly used as the metal component of the catalyst. Rh will form a complex molecule with the ligand which activates the hydroformylation reaction. Significant effort has been focused on the development of catalysts as demonstrated by U.S. Pat. Nos. 4,668,651, 5,113,022, 5,663,403, 5,728,861, among others. Unfortunately, however, this complex molecule decomposes during the reaction at a significantly high rate such that the spent or deactivated catalyst must be removed from the reactor and replaced with new, activated catalyst. In prior art systems the catalyst may be removed by conveying the catalyst via a downstream catalyst process path into the separation system 12, such as by employing a split stream from the bottom of the high boilers separation unit 18 and conveyed to suitably configured catalyst removal unit 20. For example, U.S. Pat. Nos. 4,668,651 and 5,113,022 describe a process where the liquid reaction solution is passed to a vaporizer/separator where the aldehyde product is removed via distillation in one or more states under normal, reduced or elevated pressure, and it is preferred to separation the desired aldehyde produce from the rhodium catalyst solution under reduced pressure at temperatures below 150xc2x0 C. and preferably below 130xc2x0 C. While the aldehyde product is separated in such process, the inventors have found that much of the catalyst degrades at these relatively high temperatures. Since significant effort and expense is taken to recover the catalyst and particularly the ligand compound, it is desirable and would be a significant advance in the art to provide a hydroformylation method that minimizes the degradation of the catalyst/ligand compound.
Accordingly, it is an object of the present invention to provide an improved method of producing aldehydes.
More particularly, it is an object of the present invention to provide a method of producing aldehydes using a hydroformylation reaction where the formation of high boilers are minimized.
Another object of the present invention is to provide a method of producing aldehydes by hydroformylation where degradation and/or decomposition of the catalyst, and in particular the ligand compound used in the reaction is minimized.
A further object of the present invention is to provide a method of producing aldehydes employing a low boiling point solvent, such as an aldehyde.
A related object of the present invention is to provide a method of producing aldehydes which reduces the operating cost of the production and reduces the number of unit operations needed to carry out the process thereby further reducing the operating and maintenance costs.
These and other objects and advantages of the present invention are achieved by a method of producing aldehydes wherein an olefinic compound is reacted with hydrogen and carbon monoxide in a hydroformylation reaction in the presence of a catalyst. The hydroformylation system comprising the hydroformylation reaction, and optionally additionally a downstream catalyst process path and/or separation steps, is carried out at a temperature of less than approximately 100xc2x0 C., and preferably less than approximately 85xc2x0 C., and most preferably less than approximately 80xc2x0 C., such that formation of high boilers during the hydroformylation reaction and decomposition of the catalyst are substantially minimized.
In another embodiment of the present invention a method of producing aldehydes is provided wherein an olefinic compound is reacted with hydrogen and carbon monoxide in a hydroformylation reaction in the presence of a catalyst. There is no real limitation to the activity of the catalyst, but for economic considerations it is preferred that the catalyst be selected such that it exhibits a reaction half time of approximately one hour or less at the selected reaction temperature and pressure. The hydroformylation reaction, and optionally additionally the downstream catalyst process path and/or the separation steps, is carried out at a temperature of less than approximately 100xc2x0 C., and preferably less than approximately 85xc2x0 C., and most preferably less than approximately 80xc2x0 C., wherein formation of high boilers and degradation of the catalyst, in particular the ligand, are substantially minimized.
In yet another embodiment of the present invention a method of producing aldehydes is provided wherein an olefinic compound is reacted with hydrogen and carbon monoxide in a hydroformylation reaction in the presence of a catalyst. The hydroformylation reaction, and optionally additionally the downstream catalyst process path and/or the separation steps, is carried out at a temperature of less than approximately 100xc2x0 C., and preferably less than approximately 85xc2x0 C., and most preferably less than approximately 80xc2x0 C., such that formation of high boilers and decomposition of the catalyst are substantially-minimized, and where the catalyst includes phosphite compounds which may be used in the method of the present invention. These phosphite compounds include, but are not particularly limited to, triaryl phosphites, trialkyl phosphites, arylalkyl phosphites, or any other phosphite. Bisphosphite and polyphosphite compounds or the like which have combinations of these in the same molecule are also included.
More specifically, monophosphite compounds can be divided into the two following compound groups. That is, one group of compounds comprises phosphite compounds having a cyclic structure, with phosphorus atoms contained in the cyclic structure. The other group of compounds comprises phosphite compounds that have no cyclic structure containing phosphorus atoms.
Among monophosphite compounds which can be used in the hydroformylation reaction encompassed in the present invention, those phosphite compounds represented by the following formula are preferred among the latter compounds, that is, phosphite compounds that have no cyclic structure containing phosphorus atoms.
P(OR1)(OR2)(OR3)xe2x80x83xe2x80x83(1)
Where R1, R2, and R3 are optionally C1 to C30 substituent-bearing alkyl groups, cycloalkyl groups, aryl groups, aralkyl groups, and heteroaryl groups. Examples of substituents are not particularly limited, provided that they do not inhibit the reaction, and include C1 to C20 alkyl groups, cycloalkyl groups, alkoxy groups, halogens, alkylamino groups, acyl groups, carboalkoxy groups, and hydroxycarbonyl groups.
Desirable compounds among these are organic phosphite compounds in which at least one of R1, R2, or R3 in General Formula 1 is a substituted aryl group represented by General Formula 2: 
where R4 is xe2x80x94C(R9)(R10) R11 or an optionally substituted aryl group; R9, R10, and R11 are each independently a hydrogen atom, fluorohydrocarbon group or hydrocarbon group; R4 preferably has steric hindrance as a whole equal to or greater than isopropyl groups; and R5, R6, R7, and R8 are each independently a hydrogen atom or organic group, and may also be condensed aromatic rings or hetero rings with adjacent substituents such as R6 and R7 bonded to each other.
Other monophosphite compounds which can be used in the reaction encompassed in the present invention include phosphite compounds represented by the following General Formula 3, which are phosphite compounds of the other group of compounds that have a cyclic structure, with phosphorus atoms contained in the cyclic structure. 
Where Z is a divalent organic group, and Y is an optionally substituted monovalent organic group.
Examples of bisphosphite and polyphosphite ligands which can be used in the reaction encompassed in the present invention include compounds represented by General Formula 9. 
Where Z represents the same divalent organic groups as those defined in General Formula 3 above; and R26 and R27 are each independently optionally C1 to C30 substituent-bearing alkyl groups, cycloalky groups, aryl groups, aralkyl groups, and hereroaryl groups. Examples of substituents are not particularly limited, provided they do not inhibit the reaction, and include C1 to C20 alkyl groups, cycloalkyl groups, alkoxy groups, halogens, alkylamino groups, acyl groups, acyloxy groups, and arkoxycarbonyl groups. Examples of end organic groups represented by R26 and R27 include C1 to C20 straight-chain or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, isopentyl, neopentyl, t-pentyl, and t-hexyl; C3 to C20 cycloalkyl groups such as cyclopropyl, cyclohexyl, cyclooctyl, and adamantyl; optionally substituent-bearing aryl groups such as phenyl, xcex1-naphthyl, xcex2-naphthyl, methoxyphenyl, dimethoxyphenyl, methoxycarbonylphenyl, cyanophenyl, nitrophenyl, chlorophenyl, dichlorophenyl, pentafluorophenyl, methylphenyl, ethylphenyl, dimethoxyphenyl, trifuoromethylphenyl, methylnaphthyl, methoxynaphthyl, chloronaphthyl, nitronaphthyl, and tetrahydronaphthyl; aralkyl groups such as benzyl; and heterocyclic aromatic groups such as pyridyl, methylpyridyl, nitropyridyl, pyrazyl, pyrimidyl, benzofuryl, quinolyl, isoquinolyl, benzimidazolyl, and indolyl. W is an optionally substituted m-valent hydrocarbon group, m1 and m2 are each independently an integer of 0 to 6, where m=m1+m2 has a value of 2 to 6. When m1 and m2 are each more than 2, then Z, R26 and R27 may be the same as or different from each other.
Even more desirable compounds include those in which Z in General Formula 9 is Z defined in General Formula 6 above, and compounds in which W is represented by General Formula 10. 
where R37 and R38 are each independently a C1 to C12 alkyl group, cycloalkyl group, alkoxy group, silyl group, siloxy group, or a halogen atom or hydrogen atom. Examples include hydrogen atoms, or methyl, ethyl, n-proply, isopropyl, n-butyl, methoxy, ethoxy, and n-propoxy groups, and fluorine, chlorine, bromine, or iodine atoms. R33 through R36 are each independently a C1 to C20 alkyl, cycloalkyl, alkoxy, silyl, or siloxy group, or a halogen or hydrogen atom. Examples include hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, t-pentyl, neopentyl, t-hexyl, nonyl, decyl, methoxy, ethoxy, and t-butoxy groups. Specific examples of Formula 10 include those in which R35 and R37 and/or R36 are R38 each independently bond to each other to form part of a cyclic structure consisting of 3 to 40 carbons. A specific example is 1,1-binaphthyl-2,2xe2x80x2-diyl. Further description is provided below in the detailed description of the invention.
In an even further embodiment of the present invention a method of producing aldehydes is provided wherein an olefinic compound is reacted with hydrogen and carbon monoxide in a hydroformylation reaction. A solvent is suitably added to assist in the hydroformylation reaction and the solvent is selected such that it exhibits a low boiling point which is defined as a boiling point that is equal to or greater than the boiling point of the aldehydes products. In one embodiment, the solvent is selected such that it is comprised, at least partially, of one or more aldehydes and/or alcohols such as an aldehyde or alcohol reactant, or optionally any of the aldehydes and/or alcohols formed in the hydroformylation reaction.